1. Field of the Invention
The present invention relates to a medical implantable device of the type having a hermetically sealed, radio shielded encapsulation, which is adapted to be implanted inside living tissue, and an RF-circuit positioned inside the encapsulation for communication with an RF-device outside the tissue, the RF-circuit being connectible to an antenna located outside of the encapsulation, via at least one hermetical feed through in the form of at least one conductor passed through a wall portion of the encapsulation in a liquid and gas tight manner and electrically insulated from the encapsulation.
The invention also relates to a method for connecting an RF-circuit inside a hermetically sealed, radio shielded encapsulation, to an antenna located outside the encapsulation.
2. Description of the Prior Art
It is becoming more and more common to communicate wirelessly with medical implantable devices, such as pacemakers, implantable cardioverter defibrillators (ICD's) or insulin pumps, which contain electronic circuits and are implanted inside tissue of human or animal bodies. In this way it is possible to monitor the function of the medical implantable device itself and/or an organ inside the body, e.g. the heart, to reprogram the device without removing it from the body in case the conditions should change, or to perform medical or therapeutic treatment on demand by means of the device inside the body, such as electrical shocks, so called defibrillation, to restart a heart that has stopped, or to request injection of a dose of insulin.
Up to now the most common way to accomplish this communication has been to use inductive telemetry. However, inductive telemetry has its limitations with regard to range and transmission speed. Therefore radio frequency transmission is considered to be a better alternative, i.e. to provide the medical implantable device with a radio transmitter and/or receiver (transceiver), hereinafter called a radio frequency circuit or RF-circuit, for enabling communication with a corresponding transmitter and/or receiver (transceiver), hereinafter called radio frequency device or an RF-device, outside the tissue.
However, when performing radio frequency communication the connection and shielding issues become more critical and an antenna connected to the RF-circuit is required. In order to avoid interference in the electronic circuits inside the medical device from external radiation sources, it is common practice to make the encapsulation of the medical implantable device not only gas and fluid tight, but also radio shielded. This is most easily accomplished by manufacturing the encapsulation of a metal, such as a titanium steel alloy, but it may also be accomplished by providing an electrically insulated material, such as a ceramic or a resin, with a shielding material, which can be applied as an inner or outer foil or coating or as an embedded netting. Thus, the antenna has to be positioned outside the radio shielded encapsulation, to be able to communicate with the RF-device, and a gas and liquid tight as well as electrical insulated feed through has to be formed through the wall of the encapsulation for the antenna connection. For manufacturing reasons, the encapsulation with the feed through and the RF-circuit board are manufactured separated from each other and then assembled together at a later stage.
It is always desirable to make the implantable devices as small as possible to minimize discomfort for the persons who have to carry them. This applies also to the RF-circuit board which normally has the size of only about 30-100 mm2, and it has to be positioned very close to other components inside the encapsulation. Thus, the space for accomplishing the connection between the RF-circuit board and the feed through to the antenna will be very limited. At the same time, when using radio frequencies in the UHF region, which is preferred, it is crucial that the connection will be of a good quality having low inductance and stray capacitance. Moreover, it is important that the connection from the encapsulation wall to the RF-circuit board will be shielded over as long a part of its length as possible to prevent radiation from the RF-circuit from interfering with other electronic circuits within the encapsulation. It is also advantageous to keep the distance between the actual antenna outside the encapsulation and the RF-circuit board as short as possible, i.e. to position the RF-circuit board as close as possible to the feed through and the encapsulation wall.
The above criteria create problems during assembling since traditional methods for providing reliable electric connections all have certain drawbacks. For example, soldering, resistance welding, laser welding and the like, creates heat which could damage the electronic circuits, especially since they are packed so tightly together. The lack of space also makes it difficult for equipment adapted for this kind of connecting methods, to get access to the connection. Such connections also make replacement of the RF-circuit board complicated or impossible if that should for any reason be desired. Moreover, those connection methods are quite expensive to perform since they require a separate manufacturing step as well as expensive equipment.